The field of the invention generally comprises automotive structural members and while particularly the specification herein describes what can be referred to in the automotive art as a load floor the invention is not intended to be limited thereto.
"Load floor" as known in the trade is an appellation generally applied to a core or bracing plate that is inserted into or connected with the back of a bench seat in a station wagon and intended to be folded down during use of the station wagon to carry goods. This core or bracing plate is required to accomplish several purposes. It must furnish strength for the seat back to the end that it is safe in the event of shocks and accidents and will not yield, bend or collapse. It must provide the connections to enable the seat back to be mounted in erect or angled position while the seat is being used by passengers; it must provide the needed hinge means to enable the folding of the seat back between the two positions in which it is intended to be used; it must provide anchoring means for various brackets which may be required to connect the seat back in its floor position, either alone or with other members. The core or bracing plate must be strong enough to support any kind of load which can be accommodated in the vehicle without yielding or collapsing.
Other requirements of such an article are of importance in that they complicate the fabrication and construction of the load floor. These requirements are that the load floor be light in weight, economical to manufacture so that the vehicle builder can incorporate the same into a vehicle of low selling price and that it is durable.
Until the advent of this invention load floors have been constructed of steel. It is believed that some work has been done in aluminum as well in order to attempt to lighten the load floor. In any event, metal load floors have been used universally, so far as is known.
The core or bracing plate of a seat back is a complicated article to manufacture from metal. As a result all such load floors known have been fabricated of many parts and pieces, using welding and fastening techniques. Strength is achieved by means of ribs, either pressed into the metal plate or welded onto the same. Attachment of hinges, connectors, brackets and the like complicate and increase the cost of manufacture. The need for tools, dies and fixtures for fabrication increases the capital expenditure for making these metal load floors, and where different models of vehicles call for differences in the design and construction the expenditure accelerates.
Despite the modern methods of manufacture, high speed production and the benefits of mass production, load floors in use today are heavy, expensive, and have a tendency to distort through use. When subjected to great weight over a period of time in use as a floor or considerable pressure through hard use as a seat back metal cores will bend and retain the distortion. This, of course, is undesirable.
In accordance with the invention, the load floor is formed as a blow-molded member out of polyethylene or other of the synthetic polymers that are used in blow-molding. It emerges from the mold as a completely finished article but for the need to attach the hinges, brackets and connectors. Inserts may be placed in the mold before each charge carrying nuts or other sockets which are permanently molded into the finished article and will thus receive fastening means when installation occurs.
In the case of the fabricated metal load floors, the article is a unit made out of multiple pieces and is not very pleasant in appearance. It is thus normally buried in the upholstery of the seat back, those parts which of necessity must protrude being carpeted, painted or otherwise finished. In the case of a load floor constructed in accordance with the invention, the surface of the article can be molded with any desired texture built into the mold, such as for example -- graining. Further, the plastic used can be of any desired color without difficulty. Thus, it is feasible to construct the seat back so that the floor load is exposed. This provides a hard surface for the floor when used to support goods.
It has been known to form structural members for vehicles from molded synthetic resins. Such members have been formed of fiberglass reenforced epoxy resins, either molded in forms and cured therein or applied in multiple laminas. Such members as may be subject to stress must be fabricated in situ by known techniques or constructed in much the same manner as metal members, usually manually. Production methods call for the construction of large molds into which the layers of fiberglass and the resin are alternately laid after which the article must be subjected to a cure.
Notwithstanding such techniques, it is believed that there are no members of fiberglass reenforced epoxy resins, or even of the resins themselves which are completely enclosed and hollow. This type of molding is even more expensive than metal fabrication and not as strong and durable.
Structural members for vehicles which are at the present time made of metal and which are ideally suited for the techniques of the invention are vehicle doors which must support glass panes and mechanisms for raising and lowering the same; side panels which serve as doors or vents without glass and which must be operated; any parts which are required to be strong and durable and which carry equipment and accessories.
Blow-molding as referred to herein is a technique which has been developed in relatively recent times. According to the practice which has developed a charge of plastic such as polymer which is readily converted into a plastic taffy-like consistency is extruded from a so-called head in a tubular form depending vertically from the head. This form is called a parison and the extruded amount of plastic is adjusted to equal that used in the finished article with allowance for flash and similar slight waste. The bottom end of the parison is open but may be closed by pinching before molding if needed because of the shape to result to enable some inflation before the dies close.
After the parison has been discharged completely, but while still depending from the head the opposite sections of a vertically split two-part mold are tightly brought together with the parison captured between them. The mold completely encloses the parison but for a passageway for air. This passageway may be provided by a nozzle depending from the head, it may be provided in a nozzle that is mounted to be surrounded by the closing mold at the bottom of the blow-molding machine, it may be provided by a side nozzle carried by the mold or it may be a small opening in the mold through which a fine needle or the like has been inserted after the mold parts are brought together. Air may be admitted while the parison is formed or slightly after its formation and before the mold parts are brought together in order to shape the parison more geometrically to meet the general shape into which it will eventually be formed precisely. This would be the case where the final shape is a radical change from the cylindrical form of the parison and requires the bottom end of the parison to be pinched together to enable pre-expansion.
After the mold closes, admission of air into the tubular length expands the plastic resin into the mold, the extruding process having been discontinued when the mold closed. After the plastic has set, the mold is opened, the air pressure being discontinued at any convenient time, and the finished product is removed. There is usually flash of a small amount around the parting line of the mold and this is readily trimmed off, either by means of a band saw or manually, depending upon the nature of the article. The plastic is still hot enough to enable this to be done easily and quickly.
Thereafter the process is repeated.
Obviously there is no need for layering any materials in the mold, no curing, no handling of dangerous and volatile materials, no fabricating and no requirement for metal working tools and dies. One mold does everything.
While blow-molding techniques, per se, have been known and it has even been known to blow-mold chair seats, it has not been considered feasible by those in the automotive field to whom this invention is directed to achieve by blow-molding a structural member with the strength, light weight and economy achieved by the invention.
As will be explained hereinafter, one of the features of the invention is the use of tying links which are produced by the molded article to produce connecting beams between the parallel walls, the inner surface of one wall where the indentation occurs being welded to the inner surface of the other wall at the same location. This provides unusual strength and enables the article to flex and absorb shock. The distribution of these links throughout the area of the article and especially close to places where the article will be subject to stress provides a unitary structure that can withstand great stress. It has been known in blow-molding to provide indentations of a general type described herein for ornamentation and in the course of making such indentations some may have been deep enough to touch the other wall of the article being blow-molded, but so far as known, there has not been such an article where the indentations are distributed generally throughout the article to give the article strength and to rigidify the same. Indeed it is believed that the touching of indentations in the past, if such occurred, was fortuitous and not intended to be of a nature as to positively engage and weld together. Further so far as known, the technique which has been described and comprising the formation of identations of any kind in blow-molded articles, has not been practiced in the making of structural members that are to receive the stresses and loadings to which automotive structural members are subjected.
Finally, so far as known, and in addition to that which is explained above, indented blow-molded members have not been used as automotive structural members which are required to carry and be strong enough to support and operate with automotive hardware.